I have a knocking noise that started in my poor jeep last night, it is definitley coming from the top of the engine under the valve cover, i think most likely a stuck lifter after searching the posts, but i am no mechanic. is there any way to definitely find out and possibly repair without taking it somewhere? I am handy with tools and have done many repairs, just never really any engine work besides tune ups and reg matinence......the noise increases with rpms, and does not go away when the engine warms up.... i have also heard that there are oil additives you can use to free stuck lifters, but are these just snake oil or what? I don't want to harm my engine any more, so poor jeep is not going anywhere till i fix this..... thanks in advance for any responses.

I think a stuck lifter would make hussing noise every time the piston moves up and down. hus hus hus hus and as stated above, quite noticeable loss of power since 1 of the 6 cylinders wont be firing/working.

Yeah, you should take a look before you do anything else. knocking up there sounds more like maybe a damaged spring or something? As stated, if youuhad a stuck lifter, I think youd have a pretty serious misfire going on, and I've not heard of that being an issue w/ the 4.0.

I have a knocking noise that started in my poor jeep last night, it is definitley coming from the top of the engine under the valve cover, i think most likely a stuck lifter after searching the posts, but i am no mechanic. is there any way to definitely find out and possibly repair without taking it somewhere? I am handy with tools and have done many repairs, just never really any engine work besides tune ups and reg matinence......the noise increases with rpms, and does not go away when the engine warms up.... i have also heard that there are oil additives you can use to free stuck lifters, but are these just snake oil or what? I don't want to harm my engine any more, so poor jeep is not going anywhere till i fix this..... thanks in advance for any responses.

I'd pull the valve cover off and visually inspect the rocker arms and pushrods for excessive play. You may have over tached the motor and simply bent a pushrod...it happens and it's a cheap repair ($10.00 plus a new gasket). It's possible you broke a rocker arm too but that's probably less of a factor.

Get yourself a repair manual and a remote starter. Pull off the ignition wire and rotate the motor using the remote starter. You can then troubleshoot the problem when the motor is spinning at slow speed.

The only oil additive I have had any kind of luck with in recent years has been CD-2 in the gray bottle. In my area it is only available at O'Reilly's. My beat up old Honda had a sticking lifter and it freed up and I have put 15k miles on it since that happened (181k on her total). My father got 318k miles out of a 1992 Ford Escort by religiously using that additive. I would definately start by doing what was described by MOz and then consider additives once it is fixed to prevent the problem from happening again. Good luck and keep us posted!

Just had the same exact indications on my 97Tj with the four hamsters. I pulled the whole top end apart to find the center two exhaust lifters slightly stuck. I replaced all the lifters all the pushrods and cleaned it all up. I fired it up, the sound was still there. I definetly thought that the sound was from the top but as i drove it, it got worse. Finally I was driving along and and what ever it was brove, siezed the engine and I heard it fall into the oil pan. Everyone is saying it is the rod bearing. Going to tear it apart shortly but I wouldn't drive it. Sorry I can get more into depth but I got to go to work, let me know if u want me to describe the symtoms i had better.

i have a lifter noise in my 4.0. the lifters in the 4.0 and 2.5 are low in the engine and can sound like a rod. if its in the valve cover then this is a rocker. the nut could have loosend and or needs to be tighned or adjusted. stuck lifters and collapsed lifters usualy happen with engins that have been sitting for a while or never get the oil changed

yeah, its going to my neighbors shop, he checked it out and said it sounds like a rod, but he can't be sure until he gets it into the shop....but, unfortunately they are backed up for 2 weeks cuz he was in the hospital for 13 days so it may be a while before i have my poor little jeep back, but thanks again for all the responses, very helpful and much appreciated!